WooCommerce variations custom field

gistfile1.php

//Display Fields
add_action( 'woocommerce_product_after_variable_attributes', 'variable_fields', 10, 2 );
//JS to add fields for new variations
add_action( 'woocommerce_product_after_variable_attributes_js', 'variable_fields_js' );
//Save variation fields
add_action( 'woocommerce_process_product_meta_variable', 'variable_fields_process', 10, 1 );

function variable_fields( $loop, $variation_data ) {
?>	
	<tr>
		<td>
			<div>
					<label><?php _e( 'My Custom Field', 'woocommerce' ); ?></label>
					<input type="text" size="5" name="my_custom_field[<?php echo $loop; ?>]" value="<?php echo $variation_data['_my_custom_field'][0]; ?>"/>
			</div>
		</td>
	</tr>
<?php
}

function variable_fields_js() {
?>
<tr>\
		<td>\
			<div>\
					<label><?php _e( 'My Custom Field', 'woocommerce' ); ?></label>\
					<input type="text" size="5" name="my_custom_field[' + loop + ']" />\
			</div>\
		</td>\
	</tr>\
<?php
}

function variable_fields_process( $post_id ) {
	if (isset( $_POST['variable_sku'] ) ) :
		$variable_sku = $_POST['variable_sku'];
		$variable_post_id = $_POST['variable_post_id'];
		$variable_custom_field = $_POST['my_custom_field'];
		for ( $i = 0; $i < sizeof( $variable_sku ); $i++ ) :
			$variation_id = (int) $variable_post_id[$i];
			if ( isset( $variable_custom_field[$i] ) ) {
				update_post_meta( $variation_id, '_my_custom_field', stripslashes( $variable_custom_field[$i] ) );
			}
		endfor;
	endif;
}

Unfortunately I'm not in a position I can test this right now (super busy, not even working in Wordpress at the moment). If you could post a live example I might be able to look at it for you. Otherwise you might try looking at the javascript I posted and troubleshoot from there. Grab a beer, as that was not fun to write.

Thanks so much @DesignByOnyx you have done a great job.
I have got the fields into the front end which is awesome, However I can't get content to work in them? I was wondering if they needed to be defined somehow? I don't have much code experience and was just hoping anyone can take a quick look at where I am at.
The fields created are the highlighted in pink, I'm after two things,

1. The content and editability, and
2. is the order in which they show?
   Any suggestions will be greatly appreciated...
   http://www.staging.theflowerrun.com.au/product/flower-run-bunch/

I also used the code provided by @DesignByOnyx but can't get custom field values of single product variation.
I notice that even the comment " Holds the value for the variation custom field " disappeared when I use firebug.

Hello
I did see an array of custom field values with firebug but i still can't find a way to display custom field values.
Any help would be really appreciated.
Regards.

If someone else is stuck, here is a code modification that solves the problem when variable data is not saved or displayed correctly. This is a short example, with just the number field. To be honest, I'm not sure if the JS part is needed at all. and please also note that I have tested it on WC 2.3.5

// Number Field woocommerce_wp_text_input( array( 'id' => '_purchase_price['.$loop.']', 'label' => __( 'Purchase Price', 'woocommerce' ), 'value' => get_post_meta($variation->ID, '_purchase_price', true), 'custom_attributes' => array( 'step' => 'any', 'min' => '0' ) ) ); ?> </td> '_purchase_price[ + loop + ]', 'label' => __( 'My Number Field', 'woocommerce' ), 'desc_tip' => 'true', 'description' => __( 'Enter the custom number here.', 'woocommerce' ), 'value' => $variation_data['_purchase_price'][0], 'custom_attributes' => array( 'step' => 'any', 'min' => '0' ) ) ); ?>

Hello @shirg!
Did you succeed to display custom field value for each variation on frontend?
Cheers.

Actually the code provided was working (WC 2.3) !

Hey @whoaloic

I really cannot figure out how to get the Remicorson snippets or anything like that to show up on the FRONT of my site. I saw in his tutorial he had a tiny note about it and some other people have been figuring out but I just cannot.

Yes, displaying in the front is the issue: I can display custom meta values when there's only one variation.

When products have multiple variable attributes the meta display but it is WRONG : it only display the first value found with the selected attribute, not taking into account the full variation.

Any idea ?

That worked for me:
Use the woocommerce_ajax_save_product_variations and change the variable_fields_process function.

//Save variation fields
add_action('woocommerce_ajax_save_product_variations', 'variable_fields_process', 10, 2);

function variable_fields_process($product_id) {
$variable_post_id = $_POST['variable_post_id'];
$variable_custom_field = $_POST['my_custom_field'];

foreach ($variable_post_id as $key => $value) {
    if (isset($_POST['my_custom_field'][$key])) {
        update_post_meta($value, 'my_custom_field', $variable_custom_field[$key]);
    }
}

}